Can a variable from the server be used for the "selected" default value in the SelectInput() function?

I am trying to use a numerical variable from the server as the default value for the "selectInput()" box in Shiny to no avail. There are two selection boxes, the first one is fixed, but I want the default value for the second one to be set by a variable, how can I achieve this? I tried using renderUI() and uniOutput() in different ways with no success.

library(shiny) 

ui <- fluidPage(
  uiOutput("year22"),
  selectInput("y1", label = "Start Year: ", choices = c(1900: 2024), 
              width = 100, size = 3, selectize = FALSE),
  selectInput("y2", label = "End Year: ", choices = c(1900: 2024),
              width = 100, size = 3, selected = year22, selectize = FALSE))

server <- function (input, output, session) {
    output$year22 <- renderUI({
      1963 #For simplicity I just included a number here instead of code, but I would 
           #like to use the variable 'year22' for the default value in the second 
           #selection box above
    })
}
shinyApp(ui, server)

Depending on your use case you can use e.g. a reactive to store the value for year22, then use updateSelectInput and an observer to set the selected= value for the second selectInput:

library(shiny)

ui <- fluidPage(
  selectInput("y1",
    label = "Start Year: ", choices = c(1900:2024),
    width = 100, size = 3, selectize = FALSE
  ),
  selectInput("y2",
    label = "End Year: ", choices = c(1900:2024),
    width = 100, size = 3, selected = NULL, selectize = FALSE
  )
)

server <- function(input, output, session) {
  year22 <- reactive({ 1963 })
  observe({
    updateSelectInput(
      inputId = "y2",
      selected = year22()
    )
  })
}
shinyApp(ui, server)
#> 
#> Listening on http://127.0.0.1:7692

UPDATE I can't reproduce the issue you reported in your comments. In the code below I added a textOutput to the code which outputs the value selected in the second selectInput and which shows that the input$y2 contains the selected value and no reversion of the selected= value to 1963.

library(shiny)

ui <- fluidPage(
  selectInput("y1",
    label = "Start Year: ", choices = c(1900:2024),
    width = 100, size = 3, selectize = FALSE
  ),
  selectInput("y2",
    label = "End Year: ", choices = c(1900:2024),
    width = 100, size = 3, selected = NULL, selectize = FALSE
  ),
  textOutput(
    "end_year"
  )
)

server <- function(input, output, session) {
  year22 <- reactive({
    1963
  })
  observe({
    updateSelectInput(
      inputId = "y2",
      selected = year22()
    )
  })
  
  output$end_year <- renderText({
    input$y2
  })
}
shinyApp(ui, server)